simple app for writing .txt files distractionfree

as the title says, i‘m looking for a simple app that just does this one thing. i‘m a writer and want to use a bluetoothkeyboard with a boox ereader to get something similar to a zerowriter. what it should be able to do:

• save textfiles with a name and open them to add more text
• autosave or some kind of safety
• undo/redo
• ideally fullscreen, but that‘s not a musthave
• should work on an e-ink device (so in black and white everything must be readable. i don‘t care if it looks good)

some ideas?